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Desalination using low-grade thermal energy

Desalination using low-grade thermal energy description/claims

This application claims priority to and the benefit of U.S. Provisional Application Ser. No. 60/950,076, entitled “Desalination using Low-Grade Thermal Energy”, to Nagamany Nirmalakhandan et al., filed on Jul. 16, 2007, and the specification thereof is incorporated herein by reference.

1. Field of the Invention (Technical Field)

The present invention relates to an apparatus and method for desalination.

2. Description of Related Art

Interest in the use of low grade heat sources and recovery of waste heat is growing due to increasing energy costs and declining energy sources. Examples of low grade energy sources include solar energy and heat rejected by fossil fuel-based power plants, air conditioning/refrigeration systems, and industrial processes. As a consequence of the laws of thermodynamics, thermal systems have to reject large quantities of low grade heat energy to the environment. For example, heat rejection rate of modern combined cycle power plants is almost equal to their output. Approaches to utilize waste heat to produce value added products or services can conserve limited energy sources, reduce adverse environmental impacts, and minimize overall costs.

The present invention utilizes low grade heat to operate a new desalination process. Traditional desalination processes such as reverse osmosis, electrodialysis, mechanical vapor compression, and multi-effect flash distillation require electrical energy derived from nonrenewable sources, the cost of which has increased by 10 times over the past 20 years. Recently, a new desalination process has been proposed that has the potential to run solely on low grade heat sources at around 50° C. The present invention is a modification to that process, whereby it can run around the clock, using a thermal energy storage (TES) system that enables waste heat sources and renewable energy sources to be used to drive the process with minimum reliance on grid power. TES manages variable energy demand over time, is a continuous heat source, and has a lower specific energy for desalination. The present invention, unlike the process mentioned above, enables solar collectors and photovoltaic panels to provide the energy to drive the process. The TES system can be maintained at the desired temperature using low grade waste heat from any available source.

A preferred embodiment of the present invention is described below. The embodiment is a desalination system comprising a desalination unit, a low grade heat source for powering the desalination unit and a thermal energy storage system for storing the low grade heat source and maintaining a specified temperature range. The system is able to run continuously within a specified temperature range between approximately 40-50° C. The low-grade heat source is at least partially supplied by an absorption refrigeration unit which maintains the thermal energy storage refrigeration unit at a specified temperature range. The absorption refrigeration unit operates at a pressure range of between approximately 1.4 to 15.75 kPa.

The desalination unit comprises an evaporation chamber, a condenser, a heat exchanger and one or more columns. The columns comprise a saline water column, a brine withdrawal column and a desalinated water column. The heat input to the evaporation chamber is provided by the thermal energy storage system.

The desalination system does not have a pump except for an initial starting pump. In addition, the system does not have any other moving parts.

Another embodiment of the present invention is a method of desalinating comprising the steps of operating a desalination unit, powering the desalination unit using a low grade heat source, storing the low grade heat source in a thermal energy storage unit and maintaining a specified temperature range of the low grade heat source. The desalination unit can run continuously and comprises desalinating saline water at a temperature range of approximately 40-50° C. The method can also comprise supplying the low grade heat source at least partially by an absorption refrigeration unit. The absorption refrigeration unit can also provide a cooling load. The thermal energy storage unit is maintained at a specified temperature range within the absorption refrigeration unit. Finally, the absorption refrigeration unit operates at a pressure range of between approximately 1.4 to 15.75 kPa.

Further scope of applicability of the present invention will be set forth in part in the detailed description to follow, taken in conjunction with the accompanying drawings, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.

The accompanying drawings, which are incorporated into and form a part of the specification, illustrate one or more embodiments of the present invention and, together with the description, serve to explain the principles of the invention. The drawings are only for the purpose of illustrating one or more preferred embodiments of the invention and are not to be construed as limiting the invention. In the drawings:

FIG. 1 is a schematic of a preferred embodiment of the desalination system of the present invention;

FIG. 2 is a table of model parameters used in an example simulation of mass and energy balances of a preferred embodiment;

• Provisional Patent
• Utility Patent

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